The present invention is designed to provide apparatus for detecting the presence of folded corners of sheets, as well as other abnormal thickness conditions. Sheets, and especially paper sheets, such as, for example, paper currency, experience a large amount of manual handling which quite frequently leads to bending, creasing and tearing of the paper currency as well as experiencing a general deterioration and accumulation of foreign matter which may be liquid and/or solid. The more abuse experienced by paper currency, the sooner it becomes necessary to take paper currency out of circulation.
Before newly printed paper currency is placed into circulation, it is quite stiff and, of course, clean. New or slightly used paper currency, or at least paper currency which experiences careful handling, is extremely advantageous for use in automatic dispensing equipment, such as automated 24-hour teller systems. Automated equipment of this nature is manufactured to meet tight, high-precision tolerances and will tend to malfunction or jam in the presence of unfit currency. Currency which is unfit for use in such equipment, even though quite new, is currency which has been severely folded or creased, repaired by a tape strip as a result of having been partially or completely torn through and/or currency having folded corners.
It is important to be able to differentiate between fit and unfit currency when handling such currency, for example, in day-to-day banking applications. Since the volume of currency handled by a bank on a typical day is quite large, it is extremely important to provide equipment for handling and counting such currency and to determine the fitness or unfitness or said currency at high operating speeds.
Although equipment presently exists for detecting the presence of folded corners, such equipment is either sluggish, lacks the desired sensitivity or lacks the ability to provide for instantaneous adjustment due to gradual or even relatively abrupt changes in either the mechanical or the electronic components thereof.